1. Field of the Invention
The present invention relates to a magnetic thin film recording medium and to a magnetic recording apparatus using it. More specifically, the present invention relates to a magnetic thin film recording medium and a recording apparatus which provide low noise performance and a high recording density.
2. Description of the Related Art
There have been proposed some materials for a recording medium which can provide a high recording density, including a Co alloy film coated on a pure Cr film and a Co--Ni--Pt based thin film. Some of these proposed media are in actual use. One cobalt based alloy (hereinafter referred to as Co-based alloy) magnetic thin film is a Co--Cr--Ta alloy thin film as disclosed, for example, in IEEE Transaction on Magnetics, Vol. 23, p. 122 (1987).
A thin film medium comprising a magnetic layer having a multi-layer structure has also been proposed to achieve higher output signals during reproducing (Japanese Patent Application Laid-Open No. 1-173313, Japanese Patent Application Laid-Open No. 1-217723). If a multilayer structure comprising magnetic layers and non-magnetic layers are formed by using a Co-based alloy containing Ni or a Co--Pt alloy, it is possible to obtain a higher output signal level in reproduction.
However, as described in Japanese Patent Application Laid-Open No. 3-283016, these media have a disadvantage that the noise level and bit shifting resulting from transition regions between adjacent recording bits are greater than those of conventional coated-type media. To achieve a high recording density using this type of medium, it is required to improve noise performance and to reduce bit shifting. One proposed technique to achieve this requirement is to form a magnetic recording medium having a multilayer structure provided alternately with both of Co--Cr--Ta alloy magnetic thin films and Cr alloy non-magnetic thin films.
In the case where a Co--Cr--Pt alloy is used as a material for the magnetic layers of the multilayer structure, if the number of non-magnetic layers disposed between the magnetic layers is increased while the thickness of the magnetic layers is made constant, then the noise level will be reduced, as described in IEEE Transaction on Magnetics, Vol. 26, p. 2706 (1990).
However, in conventional magnetic recording media, it is required to form a non-magnetic intermediate layer. Therefore, after forming a non-magnetic underlying layer and a magnetic layer on it, at least one Cr alloy non-magnetic metal layer is formed and then a magnetic layer is formed on it. However, this structure has difficulty in reducing medium noise in high density recording. As a result, a magnetic recording apparatus using this type of recording medium also has difficulty in increasing recording density per unit volume. Furthermore, the presence of non-magnetic intermediate layers causes an increase in the distance of a medium defined between a medium end portion confronting a magnetic head and the lower magnetic layer. Another problem is a long processing time required to form the medium. Furthermore, a number of sputtering chambers are required to form a plurality of non-magnetic intermediate layers, which results in a high cost.